1. Field of the Invention
The present invention relates to an optical pickup device and an optical disk device that perform recording and/or reproduction of information with respect to an optical recording medium such as optical disk.
2. Description of the Related Art
A recording medium that has been popular for use to record information signals includes a CD (Compact Disc) using light beams of a wavelength of about 785 nm, a DVD (Digital Versatile Disc) using light beams of a wavelength of about 660 nm, and a high-density-recording-capable optical disk performing recording and reproduction of signals using light beams of a wavelength of about 405 nm coming from a bluish-violet semiconductor laser or others (hereinafter, referred to as “high-density-recording optical disk). For recording and reproduction of information signals to/from such an optical disk, an optical pickup device has been used.
Such an optical pickup device generally uses a single objective lens, which has the design wavelength of suppressing any axial spherical aberration. A semiconductor laser used as a light source in any actual optical pickup device suffers from a variation of an oscillation wavelength caused during manufacturing, but with a CD, a DVD, and others, as long as with the design wavelength of suppressing any spherical aberration on an optical axis, the amount of spherical aberration has been permissible even if the spherical aberration is generated due to the oscillation wavelength showing a difference from the design wavelength.
The issue here is that, in an optical system of an optical pickup device for use with a so-called high-density-recording optical disk with a numerical aperture of 0.82 or larger, and the wavelength in use is of about 400 nm, i.e., short wavelength, even with a design wavelength of suppressing any axial spherical aberration, there is a problem that any variation of an oscillation wavelength caused due to manufacturing deviations or others in a semiconductor laser generates spherical aberration of an amount not permissive.
There is another problem that, when the optical system includes any component of diffractive structure, the spherical aberration to be caused due to the varying wavelength is increased in amount.
In view thereof, there needs to put the tolerance value under the strict observation in terms of the manufacturing deviations for a semiconductor laser to be used with the optical pickup device described above. This resultantly reduces the yield of the semiconductor laser, thereby preventing the reduction of the cost.
For more information, refer to Patent Document 1 (JP-A-2006-309903).